Characteristic reactions of Silver cations Ag+

Characteristic reactions of Silver cations Ag⁺

Characteristic reactions of Lead cations Pb²⁺

2. qualitative reactions of cations of analytical group 3:

Charateristic reactions of сations Ba²⁺

Characteristic reactions of strontium сations Sr²⁺

Characteristic reactions of strontium сations Ca²⁺

Characteristic reactions of Silver cations Ag⁺

Ag⁺ + NH₄OH = AgOH↓ + NH₄⁺

2AgOH↓ = Ag₂O↓ + H₂O

Ag₂O↓ + 4 NH₄OH = 2[Ag(NH₃)₂]⁺ + 2OH^- + 3H₂O or

AgNO₃ + NH₄OH = AgOH↓ + NH₄NO₃

Ag₂O↓ + 4 NH₄OH = 2[Ag(NH₃)₂]OH + 3H₂O

Add by drops ammonia solution to 1-2 drops of silver nitrate solution till precipitation formation. Observe dissolving of turbidity at adding of excess of ammonia.

Characteristic reactions of Lead cations Pb²⁺

Potassium Chromate (Dichromate) K₂CrO₄ (K₂Cr₂O₇) forms yellow precipitation PbCrO₄ with ions Pb²⁺. This sediment doesn’t dissolve in acetic and hydrochloric acids, but solutes in alkalis and nitrate acid. Conditions: pH less then 7 (in presence of acetic acid), absence of reducing agents, reduced Cr⁶⁺ till Cr³⁺ (for example, Fe²⁺), absence of cations, formed with CrO₄^2- sediments:

Pb²⁺ + CrO₄^2- = PbCrO₄↓

or 2Pb²⁺ + Cr₂O₇^2- +H₂O = 2PbCrO₄↓ +2H⁺

For example:

Pb(NO₃)₂ + K₂CrO₄ = PbCrO₄↓ +2KNO₃

or

2Pb(CH₃COO)₂ + K₂Cr₂O₇ + H₂O = 2PbCrO₄↓ + 2KCH₃COO + 2CH₃COOH

Test carrying out

Add 1-2 drops of potassium chromate or dichromate solution to 1-2 drops of lead salt solution. Yellow precipitate formed.

Characteristic reactions of Mercury cations Hg²⁺

Iodide of potassium with a cation Hg2+ gives red precipitate of mercury iodide (II):

Test-carrying out

Pour into a test tube of 1 to 2 cm³ solution of nitrate of mercury (II) and add a few drops of potassium iodide. Thus fall red precipitate of mercury iodide (II), soluble in excess of reagent. Write molecular and ion-molecular reactions.

Characteristic reactions of сations Ba²⁺

1. Potassium chromate gives with the cation of barium, a yellow precipitate of barium chromate.

Test carrying out

In a test tube with solution of salt of barium add 2 - 3 см³ solution of dichromate of potassium.

2.The flame coloration. Volatile barium salts color a flame colorless to yellow-green.

Characteristic reactions of strontium сations Sr²⁺

The flame coloration Strontium salts color a flame colorless to carmine-red.

Characteristic reactions of strontium сations Ca²⁺

1.Ammonium oxalate (NH₄)₂C₂O₄. Ammonium oxalate forms white crystalline precipitation with Calcium ions:

Ca²⁺ + C₂O₄^2- = CaC₂O₄↓

For example,

CaCl₂ + (NH₄)₂C₂O₄ = CaC₂O₄↓ + 2NH₄Cl

The precipitation is soluble in mineral acids but is insoluble in acetic acid:

CaC₂O₄↓ + 2H⁺ = Ca²⁺ + H₂C₂O₄

CaC₂O₄ ↓ + 2HCl = CaCl₂ + H₂C₂O₄

Test carrying out

Add 2-3 drops of Ammonium oxalate to 3-4 drops of Calcium salt solution.

2. Salts of calcium paint colourless flame of gas-ring in a brick-red color.
3-LW Qualitative reactions for cations of analytical group 4-5.

In notebook to prepare the report on laboratory work that includes the General characteristics of this group of ions, reaction with group reagent and private reactions of ions. To perform laboratory work (experiments, see below), to complete the report observations.

Еxperiments:

1.qualitative reactions of cations of analytical group 4: